A liquid crystal display device includes a liquid crystal panel and a lighting unit (a backlight unit) configured to supply light to the liquid crystal panel. A so-called edge light type (or a light side type) lighting unit including light emitting diodes (LEDs) disposed along an end surface of a light guide plate has been known as a lighting unit of this kind. The lighting unit is disposed behind the liquid crystal panel and configured to emit planar light toward the back surface of the liquid crystal panel.
In recent years, an edge light type lighting unit including a phosphor tube as a wavelength converting member (e.g., Patent Document 1). The phosphor tube includes quantum dot phosphors dispersed in a resin and a glass tube that is filled with the resin and sealed. In such a lighting unit, a longitudinal phosphor tube is disposed between LEDs and an end surface of a light guide plate through which light enters (a light entering surface).
When primary light rays emitted by the LEDs (e.g., blue light rays) are supplied to the phosphor tube, some of the light rays excite the quantum dot phosphors inside the phosphor tube and the rest of the light rays pass through the phosphor tube. When the quantum dot phosphors are excited by the primary light rays, the quantum dot phosphors emit secondary light rays with wavelengths different from the wavelength of the primary light rays (e.g., green light rays and red light rays). Namely, the quantum dot phosphors have a function to convert the primary light rays into the secondary light rays. The secondary light rays emitted by the phosphor tube are mixed with the primary light rays that pass through the phosphor tube. Therefore, white light rays are emitted by the phosphor tube.
Another example of a backlight is described in Patent Document 2. A planer light source, that is, the backlight described in Patent Document 2 includes LEDs, a wavelength converting member, and a light guide plate. The LEDs are configured to emit blue light rays. The wavelength converting member includes phosphors that produce fluorescence when excited by the light rays emitted by the LEDs. The light guide plate is disposed such that the wavelength converting member is between the LEDs and the light guide plate. The light rays emitted by the LEDs and the light rays emitted by the phosphors are mixed together. The mixed light rays enter the light guide plate through an end surface of the light guide plate and exit through a light emitting view surface.